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FM DXing using Spectrum-Lab as variable filter and demodulator
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| · | Bessel function products of the pilot tone at 19, 38 and 57 kHz
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| · | 57kHz RDS signal with surpressed carrier (Note: the 3x 19 kHz sits right in the gap of the surpressed carrier)
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| · | broadcaster internal used data digital signal above 60kHz, also using surpressed carrier
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| Now I tuned with 80kHz bandwith to the wanted 94,3. It is very weak and the 94,4 spectrum reaches far into our bandwith. Audio sounds awful and entirely covers the wanted 94,3 audio.
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| Now I reduced the bandwith to about 30kHz, the 94,3 tx becomes audible but with distortion, at least I am able to hear the wanted station. Fortunately German stations use a smaller deviation, stations with larger modulation become unintelligible with this narrow bandwidth
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| In this situation the Sony XDR fails to recover the wanted audio, even worse, the XDR produces now the clear audio of 94,4 but with lower volume leaving the impresion that you hear NDR-Kultur on 94,3 which is not true.
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| Once the 94,3 signal becomes stronger and exceeds a threshold, the XDR will lock on it and produce proper audio.
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| This nicely demonstrates that a good filter alone cannot remedy the problem of adjacent splatter. A smarter way of demodulation is needed.
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| These videos demonstrate some real-world reception and how to get the best out of it.
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| Please click on full screen mode when it plays to watch it in max. resolution. (via right click)
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